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  <section id="cmp0123">
<span id="policy:CMP0123"></span><h1>CMP0123<a class="headerlink" href="#cmp0123" title="Permalink to this heading">¶</a></h1>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.21.</span></p>
</div>
<p><code class="docutils literal notranslate"><span class="pre">ARMClang</span></code> cpu/arch compile and link flags must be set explicitly.</p>
<p>CMake 3.20 and lower automatically maps the <span class="target" id="index-0-variable:CMAKE_SYSTEM_PROCESSOR"></span><a class="reference internal" href="../variable/CMAKE_SYSTEM_PROCESSOR.html#variable:CMAKE_SYSTEM_PROCESSOR" title="CMAKE_SYSTEM_PROCESSOR"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_SYSTEM_PROCESSOR</span></code></a>
variable and an undocumented <code class="docutils literal notranslate"><span class="pre">CMAKE_SYSTEM_ARCH</span></code> to compile and link options
for <code class="docutils literal notranslate"><span class="pre">ARMClang</span></code>.  For example, the <code class="docutils literal notranslate"><span class="pre">-mcpu=cortex-m33</span></code> flag is added when
<span class="target" id="index-1-variable:CMAKE_SYSTEM_PROCESSOR"></span><a class="reference internal" href="../variable/CMAKE_SYSTEM_PROCESSOR.html#variable:CMAKE_SYSTEM_PROCESSOR" title="CMAKE_SYSTEM_PROCESSOR"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_SYSTEM_PROCESSOR</span></code></a> equals <code class="docutils literal notranslate"><span class="pre">cortex-m33</span></code>.  CMake requires
projects to set either variable or it raises a fatal error.  However, the
project may need to additionally specify CPU features using e.g.
<code class="docutils literal notranslate"><span class="pre">-mcpu=cortex-m33+nodsp</span></code>, conflicting with the <code class="docutils literal notranslate"><span class="pre">-mcpu=cortex-m33</span></code> added
by CMake.  This results in either link errors or unusable binaries.</p>
<p>CMake 3.21 and above prefer instead to not add any cpu/arch compile and link
flags automatically.  Instead, projects must specify them explicitly.
This policy provides compatibility for projects that have not been updated.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of this policy requires projects that use <code class="docutils literal notranslate"><span class="pre">ARMClang</span></code>
to set either <span class="target" id="index-2-variable:CMAKE_SYSTEM_PROCESSOR"></span><a class="reference internal" href="../variable/CMAKE_SYSTEM_PROCESSOR.html#variable:CMAKE_SYSTEM_PROCESSOR" title="CMAKE_SYSTEM_PROCESSOR"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_SYSTEM_PROCESSOR</span></code></a> or <code class="docutils literal notranslate"><span class="pre">CMAKE_SYSTEM_ARCH</span></code>
and it automatically adds a compile option <code class="docutils literal notranslate"><span class="pre">-mcpu=</span></code> or <code class="docutils literal notranslate"><span class="pre">-march=</span></code> and
a link option <code class="docutils literal notranslate"><span class="pre">--cpu=</span></code> based on those variables.  The <code class="docutils literal notranslate"><span class="pre">NEW</span></code> behavior
does not add compile or link options, and projects are responsible for
setting correct options.</p>
<p>This policy was introduced in CMake version 3.21.  CMake version 3.27.4
warns when the policy is not set and uses <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior.  Use the
<span class="target" id="index-0-command:cmake_policy"></span><a class="reference internal" href="../command/cmake_policy.html#command:cmake_policy" title="cmake_policy"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_policy()</span></code></a> command to set it to <code class="docutils literal notranslate"><span class="pre">OLD</span></code> or <code class="docutils literal notranslate"><span class="pre">NEW</span></code> explicitly.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of a policy is
<span class="target" id="index-0-manual:cmake-policies(7)"></span><a class="reference internal" href="../manual/cmake-policies.7.html#manual:cmake-policies(7)" title="cmake-policies(7)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">deprecated</span> <span class="pre">by</span> <span class="pre">definition</span></code></a>
and may be removed in a future version of CMake.</p>
</div>
</section>


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